Nano-scale LED element for horizontally-aligned assembly, method for manufacturing same, and horizontally-aligned assembly comprising same

ABSTRACT

The present invention relates to a nano-scale light-emitting diode (LED) element for a horizontal array assembly, a manufacturing method thereof, and a horizontal array assembly including the same, and more particularly, to a nano-scale LED element for a horizontal array assembly that can significantly increase the number of nano-scale LED elements connected to an electrode line, facilitate an arrangement of the elements, and implement a horizontal array assembly having a very good electric connection between an electrode and an element and a significant high quantity of light when a horizontal array assembly having the nano-scale LED elements laid in a length direction thereof and connected to the electrode line is manufactured, a manufacturing method thereof, and a horizontal array assembly including the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/528,046, filed May 18, 2017, which is a national phase applicationunder 35 U.S.C. § 371 of International Application No.PCT/KR2015/012252, filed Nov. 13, 2015, which claims priority to and thebenefit of Korean Patent Application No. 10-2014-0161067, filed Nov. 18,2014, the entire content of all of which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a nano-scale light-emitting diode (LED)element for a horizontal array assembly, a method of manufacturing thesame, and a horizontal array assembly including the same, and moreparticularly, to a nano-scale LED element for a horizontal arrayassembly that can significantly increase the number of nano-scale LEDelements connected to an electrode line, facilitate an arrangement ofelements thereof, and implement a horizontal array assembly having avery good electric connection between an electrode and an element and asignificantly high quantity of light when a horizontal array assemblyhaving the nano-scale LED elements laid in a length direction thereofand connected to the electrode line is manufactured, a manufacturingmethod thereof, and a horizontal array assembly including the same.

BACKGROUND ART

Light-emitting diodes (LEDs) have been actively developed since 1992when Shuji Nakamura et al. of Nichia Corporation of Japan succeeded infusing high-quality monocrystalline GaN nitride semiconductors byapplying a low-temperature GaN compound buffer layer. LEDs have asemiconductor structure formed by bonding an n-type semiconductorcrystal in which electrons are majority carriers and a p-typesemiconductor crystal in which holes are majority carriers, and asemiconductor device that converts electronic signals into light havinga desired wavelength band and emits the light. In relation to such LEDs,Korean Patent Publication No. 2009-0020869 discloses a method offabricating an LED and an LED fabricated by the same.

Such an LED semiconductor is a green material, which is called arevolution of light, because of a high light conversion efficiencythereof, very low energy consumption, a semi-permanent lifetime, andenvironmental friendliness. Recently, red, orange, green, blue, andwhite LEDs having high brightness have been developed along with thedevelopment of compound semiconductor technology, and the LEDs areapplicable to many fields, such as traffic lights, mobile phones,automobile headlights, outdoor display boards, LCD backlight units, andindoor or outdoor lights, and have been actively developed at home andabroad. In particular, since a GaN compound semiconductor having a wideband gap is used to manufacture an LED semiconductor that emits green,blue, and ultraviolet light and a blue LED element can be used tomanufacture a white LED element, many studies have been done on such aGaN compound semiconductor.

Among these series of studies, research has been actively conducted onnano-scale LED elements produced in nano or micro units in order toapply such nano-scale LED elements to lights, displays, or the like. Inthis research, attention has been focused on electrodes for applyingpower to nano-scale LED elements, electrode arrangements based onutilization objectives and for reducing space occupied by electrodes,methods of mounting nano-scale LED elements on electrodes, and the like.

In particular, methods of mounting nano-scale LED elements on electrodesstill have difficulties in that it is very difficult to place and mountnano-scale LED elements on electrodes as intended because of alimitation of a size of each of the nano-scale LED elements. This isbecause nano-scale LED elements are nano- or micro-scale devices andcannot be individually arranged and mounted in a target electrode regionwith human hands.

In addition, it is very difficult to control the number of nano-scaleLED elements included in a unit electrode region, a positionalrelationship between an electrode and the nano-scale LED elements, etc.when the nano-scale LED elements are mounted in a target electroderegion, and it is also difficult to obtain a high quantity of light dueto a limitation in the number of LED elements included in a unit areawhen the LED elements are arranged in a two-dimensional plane.Furthermore, it is further difficult to obtain a desired quantity oflight because not all nano-scale LED elements connected to two differentelectrodes can emit light without a defect such as an electrical short.

Accordingly, realizing a nano-scale LED element that can be easily laidin a length direction and mounted on a target electrode region iscritically required. According, it is possible to improve an alignmentof the mounted element to increase the number of LED elements includedper unit area of an electrode line and also to significantly improveelectrical connectivity of an electrode and the LED elements.

SUMMARY OF THE INVENTION

The present invention is designed to solve the above problems.

A first objective of the present invention is to provide a nano-scalelight-emitting diode (LED) element for a horizontal array assembly thatcan be easily laid in a length direction and mounted on a desiredelectrode region, and a manufacturing method thereof. According to thepresent invention, it is possible to improve an alignment of LEDelements mounted on a desired electrode region to significantly increasethe number of LED elements that are included per unit area of anelectrode line and significantly improve electrical connectivity betweenthe electrode and the LED elements.

A second objective of the present invention is to provide a horizontalarray assembly that can significantly increase the number of nano-scaleLED elements that are mounted per unit area of an electrode line byutilizing the nano-scale LED element according to the present invention,and that can have a good electrical connectivity between an electrodeand the nano-scale LED elements to emit light without faults and achievea desired quantity of light when power is applied to the electrode.

In order to accomplish the first objective, the present inventionprovides a nano-scale light-emitting diode (LED) element for ahorizontal array assembly including a first conductive semiconductorlayer, an active layer formed above the first conductive semiconductorlayer, and a second conductive semiconductor layer formed above theactive layer, the nano-scale LED element including an insulating filmconfigured to cover at least an outer surface of the active layer amongouter surfaces of the first conductive semiconductor layer, the activelayer, and the second conductive semiconductor layer; and a metal capformed at at least one end part of the nano-scale LED element, whereinthe metal cap extends from the one end part of the element and covers aside surface of the element, and an outer surface of the metal cap is atleast partially curved.

According to a preferred embodiment of the present invention, any one ofthe first conductive semiconductor layer and the second conductivesemiconductor layer may include at least one n-type semiconductor layer,and the other one may include at least one p-type semiconductor layer.

According to another preferred embodiment of the present invention, thenano-scale LED element may have a swab-shaped or dumbbell-shapedcross-section in a direction perpendicular to the semiconductor layers.

According to still another preferred embodiment of the presentinvention, a ratio of a surface area of the metal cap to a sectionalarea of the one end part of the nano-scale LED element may range from1:1.1 to 1:10.0.

According to another preferred embodiment of the present invention, thenano-scale LED element may have a length of 100 nm to 10 μm, and thenano-scale LED element, including the first conductive semiconductorlayer, the active layer, and the second conductive semiconductor layer,has a diameter of 100 nm to 5 μm.

According to still another embodiment of the present invention, themetal cap may partially cover an outer surface of an insulating filmformed on an outer surface of the nano-scale LED element.

In order to accomplish the first objective, the present invention alsoprovides a method of manufacturing a nano-scale LED element for ahorizontal array assembly, the method including steps of: (1) etching alaminate having a first conductive semiconductor layer, an active layer,and a second conductive semiconductor layer sequentially stacked on asubstrate so that the element has a nano- or micro-scale diameter; (2)forming an insulating film on an outer surface of the etched laminateincluding the first conductive semiconductor layer, the active layer,and the second conductive semiconductor layer; and (3) removing theinsulating film to expose a part of an outer surface including a topsurface of the second conductive semiconductor layer, forming a metalcap on the exposed outer surface of the second conductive semiconductorlayer, and then removing the substrate.

According to a preferred embodiment of the present invention, step (1)may include steps of: 1-1) manufacturing the laminate by sequentiallystacking the first conductive semiconductor layer, the active layer, andthe second conductive semiconductor layer on the substrate; 1-2) formingan insulating layer and a metal mask layer on the second conductivesemiconductor layer; 1-3) forming a polymer layer on the metal masklayer and forming a pattern on the polymer layer on a nano- ormicro-scale; and 1-4) etching the first conductive semiconductor layer,the active layer, and the second conductive semiconductor layer on anano- or micro-scale according to the pattern.

According to another preferred embodiment of the present invention, step(1) may include steps of: 1-1) sequentially stacking the firstconductive semiconductor layer, the active layer, and the secondconductive semiconductor layer on the substrate; 1-2) forming aninsulating layer and a metal mask layer on the second conductivesemiconductor layer; 1-3) forming a nano-sphere or micro-spheremonolayer film on the metal mask layer and performing self-assembly; and1-4) etching the first conductive semiconductor layer, the active layer,and the second conductive semiconductor layer on a nano- or micro-scaleaccording to a pattern.

According to another preferred embodiment of the present invention, step(3) may include steps of: 3-1) removing the insulating film to expose apartial outer surface including a top surface of the second conductivesemiconductor layer; 3-2) immersing the etched laminate in anelectrolytic plating solution and applying power to the laminate to forma metal cap on the exposed outer surface of the second conductivesemiconductor layer through plating; and 3-3) removing the substratefrom the laminate.

According to still another preferred embodiment of the presentinvention, step (3) may include steps of: 3-1) removing the insulatingfilm to expose the part of the outer surface including the top surfaceof the second conductive semiconductor layer; 3-2) immersing the etchedlaminate in an electrolytic plating solution and applying power to thelaminate to form the metal cap on the exposed outer surface of thesecond conductive semiconductor layer through plating; 3-3) forming asupport film above the metal cap and removing the substrate from thelaminate; and 3-4) immersing the laminate from which the substrate hasbeen removed in an electrolytic plating solution and applying power tothe laminate to form the metal cap on an exposed part of the outersurface including a bottom surface of the first conductive semiconductorlayer through plating and then removing the support film.

According to a preferred embodiment of the present invention, any one ofthe first conductive semiconductor layer and the second conductivesemiconductor layer may include at least one n-type semiconductor layer,and the other one may include at least one p-type semiconductor layer.

In order to accomplish the second objective, the present inventionprovides a horizontal array assembly including a base substrate; anelectrode line including a first electrode formed on the base substrateand a second electrode formed apart from the first electrode on the basesubstrate; and a plurality of nano-scale LED elements accordingconnected to both the first electrode and the second electrode.

According to a preferred embodiment of the present invention, thehorizontal array assembly may include one or more first nano-scale LEDelements connected to a top surface of one of the first electrode andthe second electrode at one side thereof and connected to a top surfaceof the other electrode at the other side thereof; a second nano-scaleLED element connected to a side surface of the first electrode at oneside thereof and connected to a side surface of the second electrodefacing the side surface of the first electrode at the other sidethereof; and a third nano-scale LED element connected to the top surfaceof one of the first electrode and the second electrode at one sidethereof and connected to the side surface of the other electrode at theother side thereof.

According to another preferred embodiment of the present invention, theplurality of nano-scale LED elements may be connected to one sidesurface of the first electrode at one sides thereof and connected to oneside surface of the second electrode facing the one side of the firstelectrode at the other sides thereof and are disposed between the twodifferent electrodes to form a multilayer.

Terms used in the present invention will be defined in the followingdescription.

In descriptions of embodiments of the present invention, it should beunderstood that when a layer, region, pattern or structure is referredto as being “on,” “above,” or “under” a substrate, another layer,another region, or another pattern, the terminology of “on,” “above,” or“under” includes both the meanings of “directly” and “indirectly” “on,”“above,” or “under.”

In descriptions of embodiments of the present invention, a “firstelectrode” and a “second electrode” include even electrode regions inwhich nano-scale LEDs may be substantially mounted or electrode regionsthat may be further included according to a method of placing theelectrodes on a base substrate.

In descriptions of embodiments of the present invention, a “connection”refers to a nano-scale LED element being in contact with a firstelectrode at one side and a second electrode at the other side. Also, an“electrical connection” refers to a nano-scale LED element being capableof emitting light when power is applied to an electrode line while thenano-scale LED is inserted and connected between two differentelectrodes.

In descriptions of embodiments of the present invention, “same,”“horizontal,” or “vertical” is not limited to physically accurate“same,” “horizontal,” or “vertical,” and includes meanings that aresubstantially considered to be “same,” “horizontal,” or “vertical.”

In descriptions of embodiments of the present invention, an “end part”of an element includes an end of the element in a length direction ofthe element and a portion of an outer surface of the element thatextends from the end.

In descriptions of embodiments of the present invention, a “horizontalarray assembly” refers to an assembly implemented such that a nano-scaleLED element is horizontally laid on a base substrate in a lengthdirection of the element and connected to two different electrodesformed on the base substrate. An example thereof is the same as shown inFIG. 1 , and the element length direction refers to a directionperpendicular to each layer included in the nano-scale LED element.

The present invention can implement a nano-scale light-emitting diode(LED) element that can be easily laid in a length direction and mountedon a desired electrode region to improve an alignment of the mountedelement. As a result, it is possible to significantly increase thenumber of LED elements that are included per unit area of an electrodeline and significantly improve electrical connectivity between theelectrode and the LED elements. The present invention can also implementa horizontal array assembly that can significantly increase the numberof nano-scale LED elements that are mounted per unit area of anelectrode line, achieve a desired quantity of light by emitting lightwithout faults when power is applied thereto due to good electricalconnectivity between the electrode and the mounted nano-scale LEDelements, increase a usage lifetime thereof due to an increase indurability of the LED elements along and a decrease in heat generation,and increase luminous efficiency due to an increase in the number ofelements. Accordingly, the present invention is applicable to variousfields such as lights, displays, etc.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of a horizontal array assemblyusing a conventional nano-scale light-emitting diode (LED) element.

FIG. 2 is an exploded perspective view of a nano-scale LED elementincluding an insulating film.

FIG. 3 is a partial perspective view of a horizontal array assemblyincluding a nano-scale LED element including an insulating film.

FIG. 4 is a perspective view of a nano-scale LED element placed betweentwo electrodes between which an electric field is formed.

FIG. 5 is a perspective view of a nano-scale LED element according to apreferred embodiment of the present invention.

FIG. 6 is a longitudinal sectional view of a nano-scale LED elementaccording to a preferred embodiment of the present invention.

FIG. 7 is a longitudinal sectional view of a nano-scale LED elementshaped like a swab according to a preferred embodiment of the presentinvention.

FIG. 8 is a longitudinal sectional view of a nano-scale LED elementshaped like a dumbbell according to a preferred embodiment of thepresent invention.

FIG. 9 is a sectional view of a horizontal array assembly according to apreferred embodiment of the present invention.

FIG. 10 is a perspective view showing a process of manufacturing anano-scale LED element according to an embodiment of the presentinvention.

FIG. 11 is a perspective view showing a process of manufacturing anano-scale LED element according to an embodiment of the presentinvention.

FIG. 12 is a perspective view of a horizontal array assembly accordingto a preferred embodiment of the present invention.

FIG. 13 is a perspective view of a horizontal array assembly accordingto a preferred embodiment of the present invention.

FIG. 14 is a perspective view showing a process of manufacturing ahorizontal array assembly according to a preferred embodiment of thepresent invention.

FIG. 15 is a plan view showing that a conventional nano-scale LEDelement performs self-alignment under an electric field.

FIG. 16 is a plan view showing that nano-scale LED elements self-alignunder an electric field according to a preferred embodiment of thepresent invention.

FIG. 17 is a perspective view of a conventional assembly having avertical structure.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

As described above, since nano-scale light-emitting diode (LED) elementscannot be individually arranged and mounted in a target electrode regionwith human hands because of a limitation of a size of each of thenano-scale LED elements, it is very difficult to arrange and mount thenano-scale LED elements on the electrode as intended. In order to solvesuch a problem, the inventor of the present invention found that anano-scale LED horizontal array assembly may be implemented in whichnano-scale LED elements are self-aligned due to an influence of anelectric field so that both ends of each of the elements are connectedto two different electrodes when power is applied to an electrode lineinto which a solution containing the nano-scale LED elements isinjected. However, the present inventor recognized that since theself-alignment of the nano-scale LED elements may be unsatisfactory dueto an electric field formed at an electrode line to which the power isapplied, the LED elements having the unsatisfactory self-alignment maybe badly arranged on an electrode line, and the number of nano-scaleLEDs that are connected to the electrode cannot be increased due to thebad arrangement. That is, there are still problems in that it is verydifficult to control the number of nano-scale LED elements included in aunit electrode region, a positional relationship between an electrodeand the nano-scale LED elements, and the like when the nano-scale LEDelements are mounted in the target electrode region, and it is alsoimpossible to obtain a high quantity of light due to a significantdecrease in the number of LED elements that can be included in the unitarea when the LED elements are poorly arranged in a two-dimensionalplane.

In detail, FIG. 1 is a partial perspective view of a horizontal arrayassembly using a conventional nano-scale LED element and shows a firstelectrode 10 formed on a base substrate 1, a second electrode 20 formedapart from the first electrode 10 on the base substrate 1, and anano-scale LED element 30 connected to the first electrode 10 and thesecond electrode 20. The nano-scale LED element 30 is connected to thetwo electrodes 10 and 20 that are different from each other, but thefirst electrode 10 is connected just up to an active layer 30 b of thenano-scale LED element 30. Accordingly, the nano-scale LED element 30cannot emit light due to an electrical short occurring when power isapplied to the first electrode 10 and the second electrode 20.

In order to solve such a problem, the present inventor attempted to usea nano-scale LED element 31 having an outer surface coated with aninsulating film (see FIG. 1 ) to implement a horizontal array assemblyin which nano-scale LED elements are horizontally arranged on anelectrode without faults. In detail, FIG. 2 is an exploded perspectiveview of a nano-scale LED element 30 including an insulating film. Anano-scale LED element of FIG. 2A includes an active layer 30 b formedabove a first conductive semiconductor layer 30 a, a second conductivesemiconductor layer 30 c formed above the active layer 30 b, and aninsulating film 30 f formed to entirely cover an outer surface of theactive layer 30 b and partially cover the first conductive semiconductorlayer 30 a and the second conductive semiconductor layer 30 c. Also, anano-scale LED element of FIG. 2B includes an active layer 30 b formedabove a first conductive semiconductor layer 30 a, a second conductivesemiconductor layer 30 c formed above the active layer 30 b, a firstelectrode layer 30 d and a second electrode layer 30 e formed below thefirst conductive semiconductor layer 30 a and above the secondconductive semiconductor layer 30 c, respectively, and an insulatingfilm 30 f formed to cover the first conductive semiconductor layer 30 a,the active layer 30 b, and the second conductive semiconductor layer 30c. As shown in FIG. 2A or 2B, when a nano-scale LED element having anouter surface coated with an insulating film is used, it is possible toprevent defects such as electrical shorts that occur when an activelayer of the element comes into contact with an electrode, but it isstill impossible to increase the number of nano-scale LED elements thatare included per unit area of the electrode because the arrangement ofthe nano-scale LED elements on the electrode is worsened due to theinsulating film, and it is also still difficult to obtain a desiredquantity of light because the nano-scale LED element is often notelectrically connected to the electrode although the nano-scale LEDelement is connected to the electrode.

In detail, FIG. 3 is a partial perspective view of a horizontal arrayassembly including a nano-scale LED element including an insulating filmand shows first electrodes 11, 12, and 13 formed on a base substrate 1,second electrodes 21 and 22 formed apart from the first electrodes 11,12, and 13 on the base substrate 1, and nano-scale LED elements 32, 33,34, and 35 connected to the first electrodes 11, 12, and 13 and thesecond electrodes 21 and 22. It can be seen that, among the nano-scaleLED elements of FIG. 3 , the LED element A 32, the LED element B 33, andthe LED element D 35 each have electrode layers or conductivesemiconductor layers in contact with the electrodes at both end partsthereof and are electrically connected to the electrodes while the LEDelement C 34 has only one side 33 d in contact with the electrode andthe other side 33 e not in contact with the electrode and is notelectrically connected to the electrode. That is, only when coordinationof conditions on a distance between two different electrodes, a lengthof a nano-scale LED element, and a thickness of both end parts that arenot coated with the insulating film on an outer surface of the elementis accomplished, a horizontal array assembly that achieves electricalconnection may be implemented. However, the conditions require finecontrol in nano or micro units, and thus it is very difficult toactually implement a target horizontal array assembly.

Also, a nano-scale LED element is simultaneously self-aligned by anelectric field between two different electrodes and connected to the twoelectrodes. The nano-scale LED element shown in FIG. 2 may not besufficiently and appropriately self-aligned because a region to beelectrically charged (i.e., an exposed part not coated with theinsulating film) has an extremely small surface area due to theinsulating film. In detail, FIG. 4 is a perspective view of a nano-scaleLED element placed between two electrodes between which an electricfield is formed. A first electrode layer 30 d and a second electrodelayer 30 e of the nano-scale LED element are negatively and positivelycharged by an electric field formed by a first electrode 10 and a secondelectrode 20, respectively. The first electrode layer 30 d and thesecond electrode layer 30 e are self-aligned toward the second electrode20 and the first electrode 10, respectively. Accordingly, the nano-scaleLED element may be connected to the first electrode 10 and the secondelectrode 20. However, since a surface area of an exposed part of thenano-scale LED element that is not coated with an insulating film islimited, the self-alignment of the nano-scale LED element by theelectric field is extremely insufficient. Accordingly, it is impossibleto align and connect the nano-scale LED element to an electrode asdesired. Also, a thickness of the electrode layer (or a conductivesemiconductor layer) and a diameter of the element should be decreasedin order to increase a surface area of a region to be electricallycharged by the electric field. This decreases the number of nano-scaleLED elements that may be included in a unit electrode area.

Furthermore, even when nano-scale LED elements are connected to theelectrode, multiple nano-scale LED elements having an insufficientelectrical connection with the electrode may be included therein. Inthis case, it is possible to significantly reduce durability of theelements due to defects generated when the nano-scale LED elements donot emit light and heat generated by high resistance of connected partsbetween the electrode and the nano-scale LED elements.

Accordingly, the present invention is intended to solve theabove-described problems by providing a nano-scale LED element for ahorizontal array assembly including a first conductive semiconductorlayer, an active layer formed above the first conductive semiconductorlayer, and a second conductive semiconductor layer formed above theactive layer. In this case, the nano-scale LED element includes a metalcap formed to cover an end part of the element and a portion of a sidepart of the element that extends from the end part, an outer surface ofthe metal cap is at least partially curved, and the metal cap is formedat one or more end parts of the nano-scale LED element. Accordingly, thenano-scale LED elements can be easily laid in a length direction andmounted on a desired electrode region, thus improving alignment of themounted elements. As a result, it is possible to significantly increasethe number of LED elements that are included per unit area of anelectrode line and significantly improve electrical connectivity betweenthe electrode and the LED elements.

In the following descriptions of the nano-scale LED element, “above” and“below” refer to a vertical upward direction and a vertical downwarddirection with respect to each layer included in the nano-scale LEDelement.

In detail, FIG. 5 is a perspective view of a nano-scale LED elementaccording to a preferred embodiment of the present invention. FIG. 5Ashows an active layer 50 b being formed above a first conductivesemiconductor layer 50 a, a second conductive semiconductor layer 50 cbeing formed above the active layer 50 b, an insulating film 50 f beingformed to cover the active layer 50 h and outer surfaces of theconductive semiconductor layers 50 a and 50 c, and a metal cap 50 ebeing formed at one end part of the element toward the second conductivesemiconductor layer 50 c. Also, FIG. 5B shows the active layer 50 bbeing formed above the first conductive semiconductor layer 50 a, thesecond conductive semiconductor layer 50 c being formed above the activelayer 50 b, the insulating film 50 f being formed to cover the activelayer 50 b and the outer surfaces of the conductive semiconductor layers50 a and 50 c, and metal caps 50 d and 50 e formed at both end parts ofthe element.

First, the conductive semiconductor layers 50 a and 50 c of thenano-scale LED element according to an embodiment of the presentinvention will be described.

Conductive semiconductor layers included in typical LED elements used inlights, displays, etc. may be used without limitation as the conductivesemiconductor layers 50 a and 50 c. According to a preferred embodimentof the present invention, any one of the first conductive semiconductorlayer and the second conductive semiconductor layer may include at leastone n-type semiconductor layer, and the other one may include at leastone p-type semiconductor layer.

When the first conductive semiconductor layer 50 a includes an n-typesemiconductor layer, the n-type semiconductor layer is made of one ormore semiconductor materials selected from among semiconductorsrepresented by the formula In_(x)Al_(y)Ga_(1−x−y)N (0≤x≤1, 0≤y≤1,0≤x+y≤1), for example, InAlGaN, GaN, AlGaN, InGaN, AlN, and InN, whichmay be doped with a first conductive dopant (e.g., Si, Ge, Sn, etc.).According to a preferred embodiment of the present invention, the firstconductive semiconductor layer 50 a may have a thickness of 1.5 to 5 μm,but is not limited thereto.

When the second conductive semiconductor layer 50 c includes a p-typesemiconductor layer, the p-type semiconductor layer is made of one ormore semiconductor materials selected from among semiconductorsrepresented by the formula In_(x)Al_(y)Ga_(1−x−y)N (0≤x≤1, 0≤y≤1,0≤x+y≤1), for example, InAlGaN, GaN, AlGaN, InGaN, AlN, and InN, whichmay be doped with a second conductive dopant (e.g., Mg). According to apreferred embodiment of the present invention, the second conductivesemiconductor layer 50 c may have a thickness of 0.08 to 0.25 μm, but isnot limited thereto.

Next, the active layer 50 b is formed above the first conductivesemiconductor layer 50 a and below the second conductive semiconductorlayer 50 c and may be formed in a single quantum well structure ormultiple quantum well structures. Active layers included in typical LEDelements used in lights, displays, etc. may be used without limitationas the active layer 50 b. A cladding layer (not shown) doped with aconductive dopant may be formed above and/or below the active layer 50b, and the cladding layer doped with a conductive dopant may beimplemented as an AlGaN layer or an InAlGaN layer. In addition, itshould be appreciated that materials such as AlGaN and AlInGaN may beused as the active layer 50 b. When an electric field is applied to theactive layer 50 b, light is created by electron-hole pair combination.According to a preferred embodiment of the present invention, the activelayer 50 b may have a thickness of 0.05 to 0.25 μm, but is not limitedthereto.

The above-described first conductive semiconductor layer 50 a, activelayer 50 b, and second conductive semiconductor layer 50 c may beincluded as essential elements of a light emitting structure. Otherphosphor layers, active layers, semiconductor layer, and/or electrodelayers may be further included above/below each of the layers.

Next, the insulating film 50 f is formed to cover at least an outersurface of the active layer 50 b among outer surfaces of the firstconductive semiconductor layer 50 a, the active layer 50 b, and thesecond conductive semiconductor layer 50 c. Even when power is directlyapplied to the outer surface of the active layer 50 b (e.g., when theactive layer is brought into contact with the electrode), the activelayer 50 b is protected due to the insulating film 50 f. Accordingly, itis possible to prevent the nano-scale LED element from beingelectrically short-circuited. Also, it is possible to prevent damage toan outer surface of semiconductor which may occur due to a collisionbetween nano-scale LED elements when the nano-scale LED elements areself-aligned by an electric field between two different electrodes, thuspreventing deterioration in durability of the nano-scale LED elements.Furthermore, the insulating film 50 f is responsible for preventing ametal cap, which will be described below, from being formed over theentire outer surface of the element including the conductivesemiconductor layer and the active layer and helping the metal cap to beformed at one end part or both end parts of the element in variousshapes and wide surface areas.

The insulating film 50 f may preferably include one or more of siliconnitride (Si₃N₄), silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), hafniumoxide (HfO₂), yttrium oxide (Y₂O₃), and titanium oxide (TiO₂). Morepreferably, the insulating film 50 f may be transparent while being madeof the above component, but is not limited thereto. When the insulatingfilm 50 f is transparent, it is possible to minimize a decrease inluminous efficiency of the element that may be exhibited when theinsulating film 50 f is coated on the element to perform theabove-described roles. According to a preferred embodiment of thepresent invention, the insulating film 50 f may have a thickness of 5 to50 nm, but is not limited thereto.

Next, the metal caps 50 d and 50 e formed at one or more end parts ofthe nano-scale LED element will be described.

Each of the metal caps partially covers a side part that extends fromthe end part in order to further increase a surface area of the end partof the nano-scale LED element while covering the end part of theelement. In this case, an outer surface of the metal cap is at leastpartially curved.

In detail, FIG. 6 is a longitudinal sectional view of a nano-scale LEDelement according to a preferred embodiment of the present invention andshows a metal cap 51 e formed at one end part of the element. In moredetail, the metal cap 51 e covers an end A₁ at one end part of theelement and also a side part A₂ connected to the end A₁, and the metalcap 51 e does not cover an insulating film 51 f, but covers an outerside surface of a second semiconductor layer 51 c. Also, a sectionaloutline of the metal cap 51 e includes a curved line, and thus an outersurface of the metal cap 51 e includes a curved surface.

When the above-described insulating film 51 f is formed to cover anouter surface of the element, which includes an outer surface of theactive layer, the metal cap 51 e may be formed to partially cover anouter surface of the insulating film 51 f.

In detail, FIG. 7 is a longitudinal sectional view of a nano-scale LEDelement according to another preferred embodiment of the presentinvention and shows metal caps 52 e, 53 e, 54 e, and 55 e formed at oneend part of the element. Inner surfaces of the metal caps 52 e and 53 e(or 54 e and 55 e) of FIGS. 7A and 7B (or FIGS. 7(c)-7(d)) are incontact with insulating films 52 f and 53 f (or 54 f and 55 f) to coversome outer surf aces S1 and S2 of the insulating films 52 f and 53 f (or54 f and 55 f) and top surfaces (ends) of second semiconductor layers 52c and 53 c (or 54 c and 55 c). Also, sectional outlines of the metalcaps 52 e and 53 e of FIGS. 7A and 7B include curved lines, and thusouter surfaces of the metal caps 52 e and 53 e include curved surfaces.

Also, a curved surface may be formed over the metal cap 54 e as in anano-scale LED element of FIG. 7C, and may be formed at a portion of themetal cap 55 e as in a nano-scale LED element of FIG. 7D. In moredetail, the nano-scale LED element of FIG. 7D shows that portions R of alongitudinal cross-section positioned in diagonal directions of theelement are curved.

In the nano-scale LED element according to the present invention, theouter surface of the metal cap is at least partially curved. Preferably,a curved portion thereof may be a region through which a virtualdiagonal extension line (1 of FIG. 7D) passes in the longitudinalcross-section of the nano-scale LED element. In detail, the virtualextension line 1 in FIG. 7D passes through the curved portion of themetal cap 55 e. In the case in which at least a portion of the outersurface of the metal cap, in particular, an outer surface of the metalcap positioned in a diagonal direction of the element in thelongitudinal cross-section of the element, is curved, the nano-scale LEDelement is easily arranged to be perpendicular to two differentelectrodes when the nano-scale LED element is self-aligned under anelectric field and connected to the electrodes. Accordingly, this may bevery advantageous in performing arrangement so that one LED elementoccupies a minimum area in the electrode region, and thus it is possibleto mount a larger number of LED elements in the electrode region.According to another preferred embodiment of the present invention, anentirety of the outer surface of the metal cap may be curved as shown inFIG. 7A to 7C.

According to still another preferred embodiment of the presentinvention, the metal cap may be formed at both end parts of thenano-scale LED element. In detail, FIG. 8 is a longitudinal sectionalview of a nano-scale LED element according to a preferred embodiment ofthe present invention and shows a first metal cap 56 d that does notcover an outer surface of an insulating film 56 f but covers a bottomsurface (an end) of a first conductive semiconductor layer 56 a of thenano-scale LED element and a side surface connected to the bottomsurface, wherein the metal cap has an outer surface that is at leastpartially curved, and a second metal cap 56 e that does not cover theouter surface of the insulating film 56 f but covers a top surface (anend) of a second conductive semiconductor layer 56 c and a side surfaceconnecting to the top surface, wherein the metal cap has an outersurface that is at least partially curved.

Also, FIG. 8B shows a first metal cap 57 d that is in contact with abottom surface of a first conductive semiconductor layer 57 a of anano-scale LED element and partially covers an insulating film 57 f,wherein the metal cap has an outer surface that is at least partiallycurved, and a second metal cap 57 e that is in contact with a topsurface of a second insulating film 57 c and partially covers theinsulating film 57 f, wherein the metal cap has an outer surface that isat least partially curved.

As described above, the metal caps included in the nano-scale LEDelement according to the present invention have outer surfaces that areat least partially curved. Accordingly, according to a preferredembodiment of the present invention, the nano-scale LED element may havea swab-shaped cross-section in a direction perpendicular to thesemiconductor layers as shown in FIG. 5A (or FIG. 6 and FIG. 7 ) or adumbbell-shaped cross-section in a direction perpendicular to thesemiconductor layer as shown in FIG. 5B (or FIG. 8 ).

Because a metal cap shaped like as described above is formed at one ormore end parts of the nano-scale LED element, a surface area of a regionof a conventional LED element that may be polarized under an electricfield significantly increases, and thus a surface of the metal cap maybe electrically charged with a larger number of positive electriccharges or negative electric charges. Accordingly, it is possible toimprove self-alignment of the nano-scale LED element on an electrodeassembly and also facilitate positional alignment. Thus, an area ratiobetween a sectional area of an end of an end part of the nano-scale LEDelement and a surface area of the metal cap may be within a range from1:1.1 to 1:10.0, preferably from 1:1.1 to 1:5, and more preferably from1:1.1 to 1:3. When the area ratio is less than 1:1.1, an improvementeffect that may be obtained by including the metal cap is insignificant,and the metal cap may not appropriately perform its function. On theother hand, when the area ratio is greater than 1:10, it may bedifficult to implement a nano-scale LED because the metal cap issignificantly increased in a long axis direction and/or a short axisdirection, and it may also be impossible to increase the number ofnano-scale LED elements that are included in a limited electrode regionbecause a volume occupied by one LED element increases.

Also, when a horizontal array assembly is implemented through anano-scale LED element having a metal cap with the above-describedshape, a horizontal array assembly that sufficiently achieves positionalalignment and electrical connectivity through target self-alignment maybe implemented as desired without needing to finely adjust conditionssuch as a width of an electrode of the assembly, a distance betweenelectrodes, a length of the nano-scale LED element, and a thickness ofan exposed part that is not coated with the insulating film of theelement to accurately coordinate the conditions. In detail, FIG. 9 is asectional view of a horizontal array assembly according to a preferredembodiment of the present invention. Nano-scale LED elements 36 and 37are connected to first electrodes 14 and 15 formed on a base substrate1, and a second electrode 24 is formed apart from the first electrodes14 and 15 on the base substrate 1. The nano-scale LED element 36, whichdoes not have a metal cap, is not electrically connected because anelectrode layer or a semiconductor layer 36 d at one side thereof is indirect contact with the first electrode 14 while an electrode layer or asemiconductor layer 36 e at the other side thereof is not in directcontact with the second electrode 24. In order to solve such a problem,it is necessary for a process of adjusting conditions such as a distancebetween the two different electrodes 14 and 24, a length of thenano-scale LED element 36, and a length of an insulating-film-uncoatedpart 36 d, and coordinating the conditions. However, it is verydifficult to coordinate all of the conditions for a horizontal arrayassembly based on a nano- or micro-scale. On the other hand, it can beseen that the element 37, which includes metal caps 37 d and 37 e,according to the present invention, among the nano-scale LED elements ofFIG. 9 , may be easily electrically connected to the two differentelectrodes 15 and 24 by the metal caps 37 d and 37 e, which are formedat both end parts, without needing to coordinate all of the conditions.

The metal caps 50 d and 50 e may be made of any one of gold (Au), copper(Cu), silver (Ag), nickel (Ni), cobalt (Co), platinum (Pt), chromium(Cr), titanium (Ti), aluminum (Al), nickel (Ni), and palladium (Pd), anoxide thereof, or an alloy of two or more thereof. When the nano-scaleLED element includes metal caps at both end parts thereof, the metalcaps may have the same or different materials.

The use of the nano-scale LED element according to the present inventionwill be described in detail. The nano-scale LED element according to apreferred embodiment of the present invention is used for a horizontalarray assembly. That is, the nano-scale LED element is suitable for anassembly in which an element is laid on a ground surface in a lengthdirection perpendicular to each semiconductor layer of the element andconnected to two different electrodes at both end parts thereof, but maynot be used for an assembly having a vertical structure in which thenano-scale LED element is mounted on the electrodes to stand upright ina length direction in three dimensions. In detail, FIG. 17 is aperspective view of a conventional assembly having a vertical structureand shows a first electrode 510 formed on a base substrate 500, a secondelectrode 520 formed above the first electrode 510, and a nano-scale LEDelement 530 disposed between the first electrode 510 and the secondelectrode 520 to stand upright in a length direction of the element inthree dimensions. Actually, except for growing nano-scale LED element ona first electrode, it is very difficult to individually connectnano-scale LED elements that are separately manufactured in the lengthdirection to stand upright in order to the assembly of the verticalstructure as shown in FIG. 17 . Also, although an electric field isformed perpendicularly to nano-scale LED elements that lie on a groundsurface of an assembly, the nano-scale LED elements may not beself-aligned to stand upright in a length direction in three dimensions.Accordingly, the nano-scale LED element according to the presentinvention may be suitable for a horizontal array assembly in which anelement is self-aligned by an influence of an electric field andconnected to two different electrodes horizontally to a ground surface.

The nano-scale LED element according to a preferred embodiment of thepresent invention, which has been described above, may be manufacturedthrough a manufacturing method thereof. However, the manufacturingmethod is not limited thereto.

The nano-scale LED element according to a preferred embodiment of thepresent invention may be manufactured by a method including steps of:(1) etching a laminate having a first conductive semiconductor layer, anactive layer, and a second conductive semiconductor layer sequentiallystacked on a substrate so that an element has a nano- or micro-scalediameter; (2) forming an insulating film on an outer surface of theetched laminate including the first conductive semiconductor layer, theactive layer, and the second conductive semiconductor layer; and (3)removing the insulating film to expose a part of an outer surfaceincluding a top surface of the second conductive semiconductor layer,forming a metal cap on the exposed outer surface of the secondconductive semiconductor layer, and then removing the substrate.

First, the step of etching a laminate having a first conductivesemiconductor layer, an active layer, and a second conductivesemiconductor layer sequentially stacked on a substrate so that anelement has a nano- or micro-scale diameter is performed as step (1).

In order to manufacture the laminate, the first conductive semiconductorlayer, the active layer, and the second conductive semiconductor layerare sequentially formed on the substrate. In detail, FIG. 10 is aperspective view showing a process of manufacturing a nano-scale LEDelement according to an embodiment of the present invention, and FIG.10A shows a first conductive semiconductor layer 210, an active layer220, and a second conductive semiconductor layer 230 stackedsequentially on a substrate 200. Any one of the first conductivesemiconductor layer 210 and the second conductive semiconductor layer230 may include at least one n-type semiconductor layer, and the otherone may include at least one p-type semiconductor layer.

The substrate 200 may include a sapphire substrate (Al₂O₃) and atransparent substrate such as glass. Also, the substrate 200 may beselected from a group including GaN, SiC, ZnO, Si, GaP, and GaAssubstrates and a conductive substrate. A square wave pattern may beformed on a top surface of the substrate 200.

A nitride semiconductor is grown on the substrate 200, and an apparatusfor the growth may include an electron beam deposition apparatus, aphysical vapor deposition (PVD) apparatus, a chemical vapor deposition(CVD) apparatus, a plasma laser deposition (PLD) apparatus, a dual-typethermal evaporator, a sputtering apparatus, and a metal organic chemicalvapor deposition (MOCVD) apparatus, but the apparatus is not limitedthereto.

A buffer layer (not shown) and/or an undoped semiconductor layer (notshow) may be formed on the substrate 200. The buffer layer is a layerfor reducing a lattice constant difference with the substrate 200 andmay be formed of at least one of GaN, InN, InGaN, AlGaN, InAlGaN, andAlInN. The undoped semiconductor layer may be implemented as an undopedGaN layer and function as a substrate on which the nitride semiconductoris grown. Only one, both, or neither of the buffer layer and the undopedsemiconductor layer may be formed. According to a preferred embodimentof the present invention, the substrate 200 may have a thickness of 400to 1500 μm, but is not limited thereto.

Detailed descriptions of the first conductive semiconductor layer 210,the active layer 220, and the second conductive semiconductor layer 230that are sequentially stacked on the substrate 200 are the same as thoseof the nano-scale LED element according to a preferred embodiment of thepresent invention, and thus will be omitted.

Next, as described above, the etching of the laminate having the firstconductive semiconductor layer, the active layer, and the secondconductive semiconductor layer sequentially stacked on the substrate sothat the element has a nano- or micro-scale diameter is performed.

To this end, according to a preferred embodiment of the presentinvention, the etching may include steps of: 1-1) sequentially stackingthe first conductive semiconductor layer, the active layer, and thesecond conductive semiconductor layer on the substrate; 1-2) forming aninsulating layer and a metal mask layer on the second conductivesemiconductor layer; (1-3) forming a nano-sphere or micro-spheremonolayer film on the metal mask layer and performing self-assembly; and1-4) etching the first conductive semiconductor layer, the active layer,and the second conductive semiconductor layer on a nano- or micro-scaleaccording to a pattern.

The insulating layer and the metal mask layer may be formed on thesecond conductive semiconductor layer (step 1-2)) after the firstconductive semiconductor layer, the active layer, and the secondconductive semiconductor layer are formed on the substrate (step 1-1)).In detail, FIG. 10B shows an insulating layer 240 and a metal mask layer250 that are sequentially formed on the second conductive semiconductorlayer 230.

The insulating layer 240 may serve as a mask for continuously etchingthe second conductive semiconductor layer, the active layer, and thefirst conductive semiconductor layer, and may use an oxide or a nitride.As a non-limiting example, the oxide or the nitride may include, but isnot limited to, a silicon oxide (SiO₂ or SiO_(x)) and/or a siliconnitride (Si₃N₄ or SiN_(x)). According to a preferred embodiment of thepresent invention, the insulating layer may have a thickness of 0.5 to1.5 μm, but is not limited thereto.

The metal mask layer 250 formed on the insulating layer 240 serves as amask layer for the etching and may use a metal that is typically used.As a non-limiting example, the metal may include, but is not limited to,chromium (Cr). According to a preferred embodiment of the presentinvention, the metal mask layer may have a thickness of 30 to 150 nm,but is not limited thereto.

Next, the step of forming a nano-sphere or micro-sphere monolayer film260 on the metal mask layer 250, and then self-assembly may be performedas step 1-3).

In detail, FIG. 10C shows a sectional perspective view of thenano-sphere or micro-sphere monolayer film 260 formed on the metal masklayer 250 of the present invention. The nano-sphere or micro-spheremonolayer film 260 is formed to serve as a mask for the etching of themetal mask layer 250, and a method of forming sphere particles may useself-assembly characteristics of a sphere. In order to form a completeone-layer structure arrangement through self-assembly of spheres, thespheres are made to float on a water surface at certain speed andperform self-assembly. Since a sphere region formed while the spheresare spread on water is small and irregular, additional energy and asurfactant may be applied to form a single sphere layer having a largeand regular arrangement. Then, the single sphere layer may be liftedonto the metal mask layer 250 to form a sphere monolayer film that isregularly arranged on a metal layer. The sphere may have a particlediameter that may be used selectively depending on a desired diameter ofa nano-scale LED element intended to be finally manufactured.Preferably, the sphere may include a polystyrene sphere, a silicasphere, etc. having a diameter of 50 to 3000 nm, but the sphere is notlimited thereto.

Next, the step of etching the first conductive semiconductor layer, theactive layer, and the second conductive semiconductor layer on a nano-or micro-scale according to a pattern may be additionally performed asstep 1-4).

FIGS. 10D to 10F show a pattering process for etching on a nano- ormicro-scale. FIG. 10D is a sectional perspective view of the nano-sphereor micro-sphere monolayer film 260 formed on the metal mask layer 250after an ashing process. Through the ashing process, sphere particlesmay be separated a certain distance from each other to achieve a desireddiameter of the LED element. Preferably, the distance may range from 50nm to 3000 nm.

The ashing process may be accomplished through a typical ashing processof a sphere monolayer film. Preferably, the ashing process may beperformed through plasma ashing and reactive ion ashing based on oxygen(O₂).

FIG. 10E shows a sectional perspective view of a metal mask layer 250′etched using a sphere particle as a mask, and FIG. 10F shows aninsulating layer 240′ etched using the etched metal mask layer 250′ as amask after a sphere particle 260′ is removed. Subsequently, as shown inFIG. 10G, the first conductive semiconductor layer, the active layer,and the second conductive semiconductor layer may be etched to a desireddepth by using the etched insulating layer 240′ as a mask. Then, asshown in FIG. 10H, an etched laminate may be manufactured by removingthe insulating layer 240′.

The etching process and the removal of the sphere particle/metal masklayer/insulating layer of FIG. 10E to 10G may be performed by a typicaletching process. In this case, a dry etching method or a wet etchingmethod may be implemented alone or in combination. In detail, a dryetching method such as reactive ion etching (RIE) or inductively coupledplasma reactive ion etching (ICP-RIE) may be used for the etchingprocess. Unlike the wet etching method, the dry etching method iscapable of unidirectional etching and is suitable to form such apattern. That is, the wet etching method performs isotropic etching inwhich etching is performed in every direction while the dry etchingmethod is capable of etching in a depth direction to form a hole. Inthis case, the hole may have a size, a distance, or the like formed in adesired pattern. In this case, when RIE or ICP-RIE is used, Cl₂, O₂, orthe like may be used as an etching gas for etching the metal mask.

According to another preferred embodiment of the present invention, step1 may include steps of: 1-1) manufacturing the laminate by sequentiallystacking the first conductive semiconductor layer, the active layer, andthe second conductive semiconductor layer on the substrate; 1-2) formingan insulating layer and a metal mask layer on the second conductivesemiconductor layer; 1-3) forming a polymer layer on the metal masklayer and forming a pattern on the polymer layer on a nano- ormicro-scale; 1-4) etching the first conductive semiconductor layer, theactive layer, and the second conductive semiconductor layer on a nano-or micro-scale according to the pattern; and 1-5) removing theinsulating layer, the metal mask layer, and the polymer layer.

In detail, step 1 may be accomplished by forming the insulating layerand the metal mask layer on the second conductive semiconductor layer,forming a typical polymer layer that may be used in typical lithographyor the like on the metal mask layer, forming a pattern on the polymerlayer on a nano- or micro-scale through a method such asphotolithography, e-beam lithography, or nano-imprint lithography,performing dry etching or wet etching, and removing the polymer layer,the metal mask layer, and the insulating layer.

Next, the step of forming an insulating film on an outer surface of theetched laminate including the first conductive semiconductor layer, theactive layer, and the second conductive semiconductor layer is performedas step (2).

In detail, FIG. 10I shows an etched laminate having an outer surfacecoated with an insulating film 270. The coating with the insulating filmmay use a method of applying an insulating material onto the outersurface of the etched laminate or immersing the etched laminate, but isnot limited thereto. Preferably, a material that may be used as theinsulating film may include one or more selected from a group consistingof SiO₂, Si₃N₄, Al₂O₃, and TiO₂, but is not limited thereto. Preferably,the insulating material may be Al₂O₃. Such an insulating material mayform the insulating film on the outer surface of the etched laminatethrough atomic layer deposition (ALD) and may form a thin film usingChemical adsorption and desorption by supplying trimethyl aluminum (TMA)and H₂O source in the form of a pulse. According to a preferredembodiment of the present invention, the formed insulating film may havea thickness of 5 to 50 nm.

Next, the step of removing the insulating film to expose a part of anouter surface including a top surface of the second conductivesemiconductor layer, forming a metal cap on the exposed outer surface ofthe second conductive semiconductor layer, and then removing thesubstrate is performed as step (3).

In step (3), a method of forming the metal cap on the outer surface ofthe second conductive semiconductor layer may use a deposition method,preferably electrochemical vapor deposition. According to a preferredembodiment of the present invention, step 3 may include steps of: 3-1)removing the insulating film to expose a part of the outer surface ofthe second conductive semiconductor layer including a top surface of thesecond conductive semiconductor layer; 3-2) immersing the etchedlaminate in an electrolytic plating solution and applying power to thelaminate to form a metal cap on the exposed outer surface of the secondconductive semiconductor layer through plating; and 3-3) removing thesubstrate from the laminate.

First, the step of removing the insulating film to expose the part ofthe outer surface of the second conductive semiconductor layer includingthe top surface of the second conductive semiconductor layer may beperformed as step 3-1).

The removal of the insulating film may be performed through a typicaletching method, and may be preferably performed through directionaletching. A detailed method thereof may be compliant with a typicalmethod well known in the art. In this case, by considering a sectionalshape, a surface area, etc. of a target metal cap that are desired, thetop surface of the second conductive semiconductor layer or even a partof a side surface connected to the top surface may be etched when theinsulating film is etched. However, it may be preferable not to exposeeven a part of the side surface of the second conductive semiconductorlayer adjacent to the active layer in order to prevent electrical shortsdue to direct contact between the electrode and the active layer. Indetail, FIG. 10J shows that only the outer surface of the etchedlaminate, excluding the top surface of the second semiconductor layer,is coated with the insulating film 270′ by removing an insulating filmof the top surface of the second conductive semiconductor layer.

Subsequently, the step of immersing the etched laminate in anelectrolytic plating solution and applying power to the laminate to forma metal cap on the exposed outer surface of the second conductivesemiconductor layer through plating may be performed as step 3-2).

The electrolytic plating solution is a solution including a material forforming a desired metal cap, and may be composed differently dependingof the material of the metal cap. As a representative example, anelectrolytic plating solution that may be used when the metal cap isformed with gold (Au) may be a mixed plating solution containing HAuCl₄,HCl, DI water, and a KAuCl₄ plating solution. In this case, theconcentration of Au may be designed differently in consideration of anelectroplating time and a size of a metal cap to be formed, and thus thepresent invention has no special limitation thereon. However,preferably, the concentration of Au may range from 0.005 wt % to 50 wt%.

The exposed outer surface of the second conductive semiconductor layermay be plated with a metal cap forming material by immersing thelaminate including the exposed surface of the second conductivesemiconductor layer in the above-described electrolytic platingsolution. In detail, the electroplating may be performed by attaching anelectrode to the substrate of the laminate and applying power to thelaminate. In order to easily form the metal cap, it is preferable thatthe substrate be a conductive substrate. A detailed electroplatingmethod may use a typical method in the art, and thus the presentinvention has no special limitation thereon. However, it is preferablethat the metal cap be formed by applying power with a −0.2 to −1.0 Vdirect current for 10 to 55 minutes. When the power is applied for lessthan 10 minutes, it may be difficult to form a metal cap having asufficient surface area and a desired sectional shape. When the power isapplied for more than 55 minutes, electrical shorts may occur in theelectrode.

The above-described metal cap forming method is not necessarily limitedto the electroplating method. The metal cap may also be formed throughthermal evaporation, e-beam evaporation, sputtering, etc.

In detail, FIG. 10K shows a metal cap 280 formed in a part of an outersurface of an end part of the element, which includes a top surface ofthe second conductive semiconductor layer that is not coated with theinsulating film through the above method.

Subsequently, when the step of removing the substrate from the laminateas shown in FIG. 10I is performed as step 3-3), a nano-scale LED elementhaving a swab-shaped cross-section may be manufactured.

Preferably, the substrate may be removed by attaching a support film toa top of the metal cap and applying a typical method such as laser liftoff (LLO). It is possible to prevent cracking of the LED element thatmay occur while removing the substrate. The support film may be apolymer epoxy or a bonding metal and have a thickness of 0.3 to 70 μm,but is not limited thereto.

According to another preferred embodiment of the present invention, inorder to manufacture an LED element having a dumbbell-shapedcross-section in which metal caps are formed at both end parts of theLED element, step (3) may include steps of: 3-1) removing the insulatingfilm to expose a part of the outer surface including the top surface ofthe second conductive semiconductor layer; 3-2) immersing the etchedlaminate in an electrolytic plating solution and applying power to thelaminate to form a metal cap on the exposed outer surface of the secondconductive semiconductor layer through plating; 3-3) forming a supportfilm above the metal cap and removing the substrate from the laminate;and 3-4) immersing the laminate from which the substrate has beenremoved in an electrolytic plating solution and applying power to thelaminate to form a metal cap on an exposed partial outer surfaceincluding a bottom surface of the first conductive semiconductor layerand then removing the support film.

The description of steps 3-1) and 3-2) is the same as that of the methodof manufacturing an LED element shaped like a swab, and thus will beomitted.

After a metal cap is formed on the exposed outer surface of the secondconductive semiconductor layer, the step of forming a support film abovethe metal cap and removing the substrate from the laminate may beperformed as step 3-3).

In detail, FIG. 11 is a perspective view showing a process ofmanufacturing a nano-scale LED element according to an embodiment of thepresent invention, and FIG. 11A shows that a support film 290 isattached to a bottom of a metal cap 280 a formed at one end part of theLED element in the laminate manufactured through step 3-2).Subsequently, in order to increase a supporting force of the LEDelement, a support polymer 291 may be filled in a space between thesupport film 290 and the laminate as shown in FIG. 11B. A supportpolymer that is well known and customarily used may be used as thesupport polymer, and thus there is no limitation in the type of supportlayer in the present invention.

Subsequently, the bottom surface of the first conductive semiconductormay be exposed as shown in FIG. 11D by removing the substrate 200 andremoving the first conductive semiconductor layer 210 that is formedbelow the substrate 200 and is not etched as shown in FIG. 11C. Theremoval of the first conductive semiconductor layer 210 that is notetched may be performed using a well-known method in the art such asultrasonic irradiation or dry etching.

Next, the step of immersing the laminate from which the substrate hasbeen removed in an electrolytic plating solution and applying power tothe laminate to form a metal cap on an exposed part of the outer surfaceincluding the bottom surface of the first conductive semiconductor layerthrough plating and then removing the support film may be performed asstep 3-4).

A detailed description of the plating through the electrolytic platingsolution is the same as described above, and thus will be omitted. Whenthe exposed surface of the first conductive semiconductor layer, whichis not coated with the insulating film, is plated with metal cap formingmaterial, a metal cap 280 b may be formed at one end part of the elementin a direction of the first conductive semiconductor layer as shown inFIG. 11E. Subsequently, when the support polymer and the support filmare removed, a nano-scale LED element having a dumbbell-shapedcross-section including the metal caps 280 a and 280 b at both end partsthereof may be manufactured as shown in FIG. 11F.

The present invention includes a horizontal array assembly including theabove-described nano-scale LED device for the horizontal array assemblyaccording to a preferred embodiment of the present invention.

A horizontal array assembly for a nano-scale LED that is horizontallyarranged according to a preferred embodiment of the present inventionmay include a base substrate, an electrode line including a firstelectrode formed on the base substrate and a second electrode formedapart from and co-planar to the first electrode, and a plurality ofnano-scale LED elements connected to both the first electrode and thesecond electrode.

In detail, FIG. 12 is a perspective view of a horizontal array assemblyfor a nano-scale LED which is horizontally arranged according to apreferred embodiment of the present invention, and shows an electrodeline 310 including a first electrode 110 formed on a base substrate 300and a second electrode 312 formed apart from the first electrode 311 onthe base substrate 300 and nano-scale LED elements 321, 322, 323, and324 connected to both the first electrode 311 and the second electrode312.

First, the base substrate 300 and the electrode line 310 including thefirst electrode 311 formed on the base substrate 300 and the secondelectrode 312 formed apart from the first electrode 311 on the basesubstrate 300 will be described.

Here, “on the base substrate” refers to the first electrode 311 and thesecond electrode 312 being formed directly above the base substrate orthe first electrode 311 and/or the second electrode 312 being formedapart from the base substrate. The base substrate serves as a supportingbody for the horizontal array assembly. As long as an electrode can betypically formed on a base substrate, the base substrate may be used asthe base substrate 300 according to the present invention without limit.As a non-limiting example, the base substrate 300 may be any one of aglass substrate, a quartz substrate, a sapphire substrate, a plasticsubstrate, and a foldable flexible polymer film. More preferably, thesubstrate may be transparent. An area of the base substrate has nolimitation and may be changed in consideration of areas of the firstelectrode and the second electrode that will be formed on the basesubstrate, a size of a nano-scale LED element connected to the firstelectrode and the second electrode, and the number of nano-scale LEDelements that are connected. Preferably, the base substrate may have athickness of 100 μm to 1 mm, but is not limited thereto.

The first electrode 311 and the second electrode 312 may be made of amaterial that is typically used as an electrode. As a non-limitingexample, the first electrode 311 and the second electrode 312 may beindependently made of one or more metal materials which are selectedfrom a group consisting of aluminum, titanium, indium, gold, and silveror one or more transparent materials which are selected from a groupconsisting of Indium Tin Oxide (ITO), ZnO: Al, and a CNT-conductivepolymer composite. When there are two or more types of electrodematerials, the first electrode and/or the second electrode maypreferably have a structure in which the two or more types of materialsare stacked. More preferably, the first electrode and/or the secondelectrode may have a structure in which two types of materials, i.e.,titanium and gold, are stacked. However, the materials of the firstelectrode and/or the second electrode are not limited to the abovedescription. Also, the materials of the first electrode and/or thesecond electrode may be the same or different from each other.

A separated space, sizes, and detailed arrangement of the firstelectrode and the second electrode may be designed differently dependingon a purpose thereof, and may be variously modified into all imaginablestructural arrangements such as a vertical or alternate arrangement oftwo different electrodes, depending on the purpose.

According to a preferred embodiment of the present invention, thehorizontal array assembly may include one or more first nano-scale LEDelements connected to a top surface of one of the first electrode andthe second electrode at one side thereof and connected to a top surfaceof the other electrode at the other side thereof; a second nano-scaleLED element connected to a side surface of the first electrode at oneside thereof and connected to a side surface of the second electrodefacing the side surface of the first electrode at the other sidethereof; and a third nano-scale LED element connected to the top surfaceof one of the first electrode and the second electrode at one sidethereof and connected to the side surface of the other electrode at theother side thereof. In detail, the horizontal array assembly of FIG. 12includes the first nano-scale LED elements 321 and 322 connected to thetop surface of one of the first electrode 311 and the second electrode312 at one sides thereof and connected to the top surface of the otherelectrode at the other sides thereof, wherein first nano-scale LEDelements 321 and 322 have a swab-shaped cross-section and adumbbell-shaped cross-section; the second nano-scale LED element 323connected to the side surface of the first electrode 311 at one sidethereof and connected to the side surface of the second electrode 312facing the side surface of the first electrode 311 at the other sidethereof; and the third nano-scale LED element 324 connected to the topsurface of the first electrode 311 at one side thereof and the sidesurface of the second electrode 312 at the other side thereof.

Also, the above-described second nano-scale LED element may be disposedbetween two different electrodes to form a multilayer, and thus it ispossible to significantly increase the number of nano-scale LED elementsthat are included per unit electrode area. In addition, when a metal caphaving a cross-sectional shape according to the present invention isformed at one or both end parts of a nano-scale LED element, the elementmay be rotated in a separated space between the electrodes by anelectric field and connect to side surfaces of the electrodes, and thusit is possible to easily make a length direction of the element beapproximately perpendicular to side surfaces of the electrodes.Accordingly, a volume occupied by one LED element decreases, and a spacein which other nano-scale LED elements can be disposed increases. Thus,it is possible to implement a horizontal array assembly having a goodquantity of light by including a larger number of nano-scale LEDelements in the space. To this end, according to a preferred embodimentof the present invention, a plurality of nano-scale LED elementsincluded in a horizontal array assembly may be connected to one sidesurface of a first electrode at one sides thereof and one side surfaceof a second electrode facing the one side of the first electrode at theother sides thereof, and also may be disposed between two differentelectrodes to form a multilayer.

In detail, FIG. 13 is a perspective view of a horizontal array assemblyaccording to a preferred embodiment of the present invention and shows afirst electrode 311 formed on a base substrate 300, a second electrode312 formed apart from the first electrode 311 on the base substrate 300to have a side surface II facing a side surface I of the first electrode311, and a plurality of nano-scale LED elements 325 and 326 brought intocontact with the side surface I of the first electrode 311 at one endsthereof and the side surface II of the second electrode 312 at the otherends and disposed between the two electrodes to form a multi-layer. Whena horizontal array assembly is implemented as shown in FIG. 13 , it ispossible to implement a horizontal array assembly that emits asignificantly high quantity of light by including a large number ofnano-scale LED elements in a limited electrode region.

The above-described horizontal array assembly according to a preferredembodiment of the present invention may be manufactured by amanufacturing method to be described below, but is not limited thereto.

A horizontal array assembly according to a preferred embodiment of thepresent invention may be manufactured by a method including steps of:(a) forming a first electrode on a base substrate and forming a secondelectrode apart from the first electrode on the base substrate; (b)providing a plurality of nano-scale LED elements, which include thenano-scale LED element for a horizontal array assembly according to thepresent invention, and a solvent to the first electrode and the secondelectrode; and (c) applying power to the first electrode and the secondelectrode to self-align the nano-scale LED elements so that thenano-scale LED elements are brought into contact with the firstelectrode at one ends thereof and brought into contact with the secondelectrode at the other ends.

In step (a), descriptions of the base substrate and the electrode arethe same as described above. A method that is well known and customarilyused in the art may be used to form the electrode on the base substrate,and thus the present invention has no special limitation thereon.

Next, the step of providing a plurality of nano-scale LED elements and asolvent to the first electrode and the second electrode is performed asstep (b).

In detail, FIG. 14 is a perspective view showing a process ofmanufacturing a horizontal array assembly according to a preferredembodiment of the present invention, and FIG. 14A shows nano-scale LEDelements 130 and a solvent 140 that are provided to the first electrode110 formed on the base substrate 100 and the second electrode 120 formedapart from the first electrode 110 on the base substrate 100.

The present invention has no limitation on a method of providing thenano-scale LED elements and the solvent to the first electrode and thesecond electrode. The nano-scale LED elements and the solvent may besimultaneously or sequentially provided regardless of their order. It ispossible to mount the nano-scale LED elements on a target electroderegion in a concentrated way by preferably providing the solvent afterproviding the nano-scale LED elements.

The solvent may preferably be one or more selected from a groupconsisting of acetone, water, alcohol, and toluene, and may morepreferably be acetone. The type of solvent is not limited to the abovedescription. As long as a solvent can be easily evaporated while notphysically or chemically affecting the nano-scale LED elements, anysolvent may be used without limitation.

Preferably, 0.001 to 100 parts by weight of the nano-scale LED elementsmay be provided per 100 parts by weight of the solvent. When less than0.001 parts by weight of the nano-scale LED elements are provided, thenumber of nano-scale LED elements connected to an electrode is small andthus it may be difficult for an ultra-small LED electrode assembly tonormally function. Accordingly, a solution should be added or dropped inorder to overcome the difficulty. When more than 100 parts by weight ofthe nano-scale LED elements are provided, it is possible to disturbalignment of each of the nano-scale LED elements.

Next, the step of applying power to the first electrode and the secondelectrode to self-align the nano-scale LED elements so that thenano-scale LED elements are brought into contact with the firstelectrode at one ends thereof and brought into contact with the secondelectrode at the other ends is performed as step (c).

In detail, when the power is applied to the first electrode 110 and thesecond electrode 120 as shown in FIG. 14B, the nano-scale LED elements130 perform self-alignment such as rotation or movement. Accordingly, itis possible to implement a horizontal array assembly in which thenano-scale LED elements 130 are connected to the first electrode 110 andthe second electrode 120 such that one ends of the elements are broughtinto contact with the first electrode 110 and the other ends of theelements are brought into contact with the second electrode 120.

When the nano-scale LED elements are self-aligned according to apreferred embodiment of the present invention, it is possible to enhancepositional alignment and electrode connectivity. In detail, FIG. 15 is aplan view showing that conventional nano-scale LED elements areself-aligned under an electric field. When power is applied to a firstelectrode 113 and a second electrode 123 that are formed apart from eachother on a base substrate 100, a nano-scale LED element 133 is rotatedby an angle a so that both ends thereof move toward differentelectrodes. As shown in FIG. 15 , since surface areas of both end partsof the nano-scale LED element 133, which is not coated with aninsulating film, are very small, an influence caused by an electricfield may be insignificant, and thus a greater electric field should beformed for the purpose of a change in position, such as movement orrotation of the nano-scale LED element 133. Also, when an outer surfaceof an exposed part that is not coated with the insulating film, inparticular, an outer surface positioned in a diagonal direction of theelement in a cross-section, is not curved, it may be difficult for theelement to be oriented perpendicular to a surf ace of an electrode whenone end part of the element is brought into contact with the electrode.On the other hand, FIG. 16 is a plan view showing that nano-scale LEDelements are self-aligned according to a preferred embodiment of thepresent invention. When power is applied to a first electrode 111 and asecond electrode 131 that are formed apart from each other on a basesubstrate 100, a nano-scale LED element 121 (121 a, 121 b, 121 c) isrotated by an angle β so that both ends thereof move toward differentelectrodes. In this case, the nano-scale LED element 121 as shown inFIG. 16 may be more affected by an electric field by including metalcaps with significantly enhanced surface areas at both end partsthereof. Accordingly, it is possible to facilitate a change in position,such as movement and rotation, of the nano-scale LED element even undera low electric field. Also, when a part of an outer surface of the metalcap, preferably, an outer surface of the metal cap positioned indiagonal directions of the electrode in the cross-section of theelectrode, are curved, it is possible to easily perform positionalalignment so that two different electrode surfaces are perpendicular toa length direction of the element, and thus a larger number ofnano-scale LED elements can be included in a limited area of thehorizontal array assembly.

An electric field needed for self-alignment of the nano-scale LEDelements may be formed by applying the power to the first electrode andthe second electrode. The power may be direct current or alternatingcurrent, and may be changed in consideration of an aspect ratio of thenano-scale element, and thus the present invention has no speciallimitation thereon.

The technical spirit of the present invention has been specificallydescribed with reference to the preferred embodiments, but it should benoted that the embodiments are provided only for illustration and notfor limitation. Also, it should be understood by those skilled in theart that various modifications can be made without departing from thescope of the preset invention.

The invention claimed is:
 1. A light-emitting element comprising: afirst semiconductor layer; a second semiconductor layer; an active layerbetween the first semiconductor layer and the second semiconductorlayer; and an electrode layer directly on at least one of the firstsemiconductor layer or the second semiconductor layer, wherein theelectrode layer comprises a first surface contacting the firstsemiconductor layer or the second semiconductor layer, and a secondsurface opposite the first surface, and wherein the second surface has acurved portion in one direction in which the first semiconductor layer,the active layer, and the second semiconductor layer are arranged,wherein the light-emitting element extends in the one direction, thecurved portion terminating at a location adjacent to one of the firstsemiconductor layer or the second semiconductor layer that contacts thefirst surface of the electrode layer.
 2. The light-emitting element ofclaim 1, further comprising an insulating film covering at least aportion of an outer surface of the first semiconductor layer, the activelayer and the second semiconductor layer.
 3. The light-emitting elementof claim 2, wherein at least a portion of the insulating film directlycontacts the electrode layer.
 4. The light-emitting element of claim 3,wherein at least a portion of the electrode layer contacts at least aportion of an upper surface and a side surface of the insulating film.5. The light-emitting element of claim 2, wherein the electrode layerfurther comprises a side surface between the first surface and thesecond surface, and at least a portion of the side surface of theelectrode layer is not covered by the insulating film.
 6. Thelight-emitting element of claim 2, wherein the first surface of theelectrode layer comprises a first portion contacting an upper surface ofthe first semiconductor layer or the second semiconductor layer, and asecond portion covering a side surface of the first semiconductor layeror the second semiconductor layer.
 7. The light-emitting element ofclaim 6, wherein the second portion is spaced from the insulating film.8. The light-emitting element of claim 6, wherein the second portioncontacts the insulating film.
 9. The light-emitting element of claim 6,wherein at least a portion of the insulating film is located between theside surface of the first semiconductor layer or the secondsemiconductor layer and the second portion of the electrode layer.
 10. Adisplay device comprising: a base substrate; a first electrode on thebase substrate; a second electrode on the base substrate and spaced fromthe first electrode; and a light-emitting element on the first electrodeand the second electrode, wherein the light-emitting element comprises afirst semiconductor layer, a second semiconductor layer, an active layerbetween the first semiconductor layer and the second semiconductorlayer, and an electrode layer directly on at least one of the firstsemiconductor layer or the second semiconductor layer, wherein theelectrode layer of the light-emitting element comprises a first surfacecontacting the first semiconductor layer or the second semiconductorlayer, and a second surface opposite the first surface, wherein thesecond surface has a curved portion in one direction in which the firstsemiconductor layer, the active layer, and the second semiconductorlayer are arranged, and wherein the light-emitting element extends inthe one direction, the curved portion terminating at a location adjacentto one of the first semiconductor layer or the second semiconductorlayer that contacts the first surface of the electrode layer of thelight-emitting element.
 11. The display device of claim 10, furthercomprising an insulating film covering at least a portion of an outersurface of the first semiconductor layer, the active layer and thesecond semiconductor layer.
 12. The display device of claim 11, whereinthe electrode layer further comprises a side surface between the firstsurface and the second surface, and at least a portion of the sidesurface of the electrode layer is not covered by the insulating film.13. The display device of claim 11, wherein the first electrode and thesecond electrode extend in a first direction, the first electrode andthe second electrode being spaced from each other in a second direction,and the light-emitting element is on the first electrode and the secondelectrode so that the one direction of the light-emitting element isparallel to the second direction.
 14. The display device of claim 13,wherein a length of the light-emitting element measured in the seconddirection is greater than a distance between the first electrode and thesecond electrode.
 15. The display device of claim 14, wherein a firstend portion of the light-emitting element is on the first electrode anda second end portion of the light-emitting element is on the secondelectrode.
 16. The display device of claim 13, wherein an upper surfaceof the first electrode and the second electrode is located higher thanthe light-emitting element.
 17. The display device of claim 13, furthercomprising a third electrode extending in the second direction, and afourth electrode extending in the second direction and spaced from thethird electrode in the first direction, wherein the first electrode andthe second electrode are between the third electrode and the fourthelectrode.
 18. The display device of claim 17, wherein the firstelectrode is electrically connected to the third electrode, and thesecond electrode is electrically connected to the fourth electrode. 19.The display device of claim 13, wherein at least a portion of a sidesurface of the light-emitting element does not directly contact thefirst electrode and the second electrode.
 20. The display device ofclaim 10, wherein the second electrode is on the first electrode, andthe light-emitting element is between the first electrode and the secondelectrode so that the one direction of the light-emitting element isperpendicular to an upper surface of the base substrate.
 21. Thelight-emitting element of claim 1, wherein the electrode layer does notoverlap a side surface of the active layer.
 22. The display device ofclaim 10, wherein the electrode layer of the light-emitting element doesnot overlap a side surface of the active layer of the light-emittingelement.